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Muscle Soreness from lactic acid and muscle fiber tears

Muscle Soreness Vs. Injury: Know the Difference

Muscle Composition

If you’ve been bodybuilding for very long, you’ve probably experienced muscle soreness and maybe even muscle injury. Knowing the difference can be extremely important to get the most out of your workout routine without going too far and causing real damage.

Here, we’ll talk about how muscles work and what they’re made of with a focus on what causes muscle soreness and muscle injury. We’ll also talk about how to tell the difference between muscle soreness and muscle injury and what to do for each.

An Introduction to How Your Muscles Work

Before we talk about muscle soreness and muscle injury, let’s take some time learning about the anatomy of muscles. That will help us understand why muscles get sore and when that soreness becomes something to worry about. If you’ve already studied up on your anatomy and physiology and just need some practical workout advice, feel free to skip ahead.

Muscle Fiber Contraction


You can think of your muscles as like a rope. It looks like one unit but if you look closer it’s made up of bundles of smaller threads. A “muscle” is a collection of “fascicles” which are collections of “fibers.” Muscle fibers are made up of smaller units called “sarcomeres.”

Sarcomeres are the level at which the action happens. We won’t get much deeper into it, but proteins in the sarcomeres repeatedly grab onto the muscle fiber, reach, let go, and grab on again, similar to climbing up a rope or a pole. This causes the sarcomeres to get shorter which leads to muscle contraction.

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Energy Needs

All of this action takes energy. When your body generates energy it’s just like when an engine generates energy – energy is produced, but there are byproducts. Those byproducts aren’t dangerous if they’re allowed to be vented out.

How your muscles generate energy is a very complicated process that we won’t get into here. For our uses, let’s just say that energy is created and the “exhaust” created is called Lactic Acid.

Muscle Injury

The Difference Between Muscle Soreness and Muscle Injury

A good rule of thumb is that generalized  “muscle soreness” is okay and acute “muscle pain” is bad. Another good rule of thumb is that if discomfort is delayed it’s okay and if it’s sudden it’s bad.

If you want more than just rules of thumb, keep reading. We’ll talk more about how to tell the difference between soreness and injury and what causes each.

Muscle Soreness

Muscle Soreness

Muscle soreness after a workout is normal. In fact, it’s a good thing, as long as you know how to deal with it. It’s caused by two main things, and both of them are things that we touched on in the “Introduction to How Muscles Work.”

The first major cause of muscle soreness is microscopic damage to the parts of the muscle. Remember the proteins in the sarcomere that climb the muscle fiber to contract the muscle bundle? Those proteins can actually break off during exercise.

If you have studied bodybuilding or hung out around the gym a lot, you’ve probably heard the buzz about protein, even after a workout. That’s because your body can use that protein to repair normal damage to muscles that can occur during exercise.

The second major cause of muscle soreness is a build-up of lactic acid in the muscles. Lactic acid, if you’ll remember from above, is the muscles’ “exhaust” from using energy. 

Like exhaust from your car building up in the garage, it’s not a problem as long as you turn the car off and allow the exhaust to escape. So, when your muscles are burning from a workout, give them a rest. Your blood will eventually carry away that built up lactic acid and you and your muscles will be fine.

Whether it’s microscopic damage, lactic acid buildup, or both causing your main soreness, there are a few easy ways to tell that it’s not something more serious. 

The first is when and how you noticed it. If you woke up the next day feeling sore, it’s regular soreness. The second is how it feels. If it’s a general ache over a large area, it’s regular soreness.

Muscle Injury Fiber Tendon Tear

Muscle Injury

Muscle injury is not normal and it’s not good. Depending on the severity, you might be able to rest it off and recover or you might want to have it looked at. Like muscle soreness, muscle injury has two main causes, but we only touched on one of them above.

In the “Introduction to How Muscles Work,” we said that muscles are made up of collections of muscle fibers. These individual fibers can actually break during a workout. If you notice this early and stop in time it’s not a problem. Pushing yourself further can lead to more serious muscle tearing, however.

The other main cause of muscle injury is one that we didn’t discuss above but requires little introduction. Your muscles are attached to your bones. However, doing an exercise that your body isn’t ready for or doing an exercise incorrectly can strain tendons. Those are the fibrous bands that connect your muscles to your bones. 

There are a couple of ways that potentially serious muscle injury feels different from more normal muscle pain. The first is when it sets on. If the pain sets on shortly after or even during exercise, it’s probably a bad sign. If it sets on during an exercise, you might have noticed it before it caused any problems. Try doing the exercise slowly with less weight as a test.

The other major way to tell the difference is through the area of the pain. With muscle soreness, the pain should be dull and spread out. To indicate where it is, you might use a whole hand. With muscle injury, the pain may be sharp and will likely be in a very small area that you can point to.

The final test comes a day or so later. If the discomfort that you felt – and probably still feel – was due to muscle injury, the area may appear bruised the next day.

Muscle Pain Soreness and Injury Indicators

What to Do

So, you’ve determined whether you’re dealing with run-of-the-mill muscle soreness or potentially serious muscle injury. What do you do now?

Muscle Soreness

If you notice muscle soreness the day after a workout, pat yourself on the back. It means you had a good workout and you didn’t hurt yourself. However, it’s never too late to hurt yourself. Both of the problems that cause healthy muscle soreness can become more serious if you don’t cool it.

That doesn’t mean that you can’t exercise today – just exercise a different muscle group. Whole body ache? Take the day off and plan to do less-strenuous full body exercise next time so that you can cut your recovery time and double your workout time.

As for easing the pain, gentle massaging can help as can light aerobic activity. Think stretching for the upper body, walking or light jogging for the lower body, and yoga for full-body aches. All of these activities encourage blood flow to the area, which can quicken healing.

Muscle Pain

If you think you pulled something – or even tore something – it still might not be time to call the paramedics. If you can still do basic activities, if the pain isn’t too bad, and if the swelling isn’t too brutal, it might not be that bad. Still, avoid exercises that target or use that area. It might start feeling better in a few days.

If you can’t do regular activities, the pain is intense, or you’re alarmed about bruising – or if milder symptoms don’t go away after a few days – take it to the clinic.

While you’re thinking it over, practice R.I.C.E. Rest the area, apply ice, apply gentle compression, and elevate the injured area.

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Parting Thoughts

The best way to make the most of your workouts are to alternate workout areas, take cooldown days when you need them, and to not push yourself too hard or too fast. Also, make sure that your diet has plenty of protein and that you practice both aerobic and anaerobic exercise in your routine.

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